Fast-switching frequency synthesizers play a special role in many systems that require the speed, such as automatic-test-equipment (ATE) systems, setups for antenna and radar-cross-section (RCS) measurements, and even in radar and electronic-warfare (EW) trainers. To fill those needs, longtime frequency synthesizer specialist Programmed Test Sources (Littleton, MA) has developed a variety of different solutions to 6.4 GHz.

Model PTS 6400 is the company's highest-frequency unit, with range of 1 to 6400 MHz and output levels from –3 to +7 dBm. In addition to the direct-analog architecture, the PTS 6400 includes a direct-digital synthesizer (DDS) for achieving fine frequency steps (1 Hz) as well as phase-continuous switching. The switching speed is a function of the step size, with switching speed on the order of 1 µs for small steps (100 kHz) to 20 µs for large steps (1 GHz). Spurious levels are a low –60 dBc from 1 to 3200 MHz and –55 dBc from 3200 to 6400 MHz. Harmonics are –30 dBc or less, and phase noise is –99 dBc/Hz offset 100 Hz from the carrier and –116 dBc/Hz offset 10 kHz from the carrier, with a noise floor of –136 dBc/Hz.

For many wireless applications, such as cellular/PCS and wireless-local-area network (WLAN) testing, the PTS 3200 (Fig. 1)features a frequency range of 1 to 3200 MHz with 1-Hz frequency resolution and phase-continuous switching courtesy of the integral DDS. The PTS 3200 provides output levels from +3 to +13 dBm with ±0.7 dB flatness. The frequency switching speed ranges from 1 µs for small steps (100 kHz) to 20 µs for large

steps (1 GHz). Spurious levels are –60 dBc through 1600 MHz and –55 dBc from 1600 to 3200 MHz. Harmonics are –30 dBc or less, and the phase noise is equivalent to that of the PTS 6400 at –99 dBc/Hz offset 100 Hz from the carrier and –116 dBc/Hz offset 10 kHz from the carrier, although the noise floor drops to a slightly higher –130 dBc/Hz.

A lower-frequency example of the firm's synthesizer lines is model PTS 1600 (Fig. 2), with a frequency range of 1 to 1600 MHz and 1-Hz frequency resolution. Like the PTS 3200, it provides output levels from +3 to +13 dBm with ±0.7 dB flatness. The phase noise is –105 dBc/Hz offset 100 Hz from the carrier and –122 dBc/Hz offset 10 kHz from the carrier, with a noise floor of –142 dBc/Hz.

The synthesizers can be equipped with either a temperature-controlled-crystal-oscillator (TCXO) reference or a more stable oven-controlled-crystal oscillator (OCXO) reference. The synthesizers can be controlled by the front panel or via remote programming using the parallel port for TTL-level binary-coded-decimal (BCD) commands or optionally via GPIB. The company recently expanded its custom capabilities based on specific requirements.